HK1176031B - System and method for air purification using enhanced multi-functional coating based on in-situ photocatalytic oxidation and ozonation - Google Patents

Description

Air purification system and method using enhanced multifunctional coating based on in situ photocatalytic oxidation and ozonation

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to U.S. provisional application No. 61/457,058, filed on 12/17/2010, and the disclosure of which is incorporated herein by reference.

Technical Field

The invention relates to an air purification system and method based on in-situ photocatalytic oxidation and ozonation. In particular, the present invention relates to systems and methods thereof that include an enhanced multifunctional coating having photocatalytic activity in the presence of sufficient ozone supply and UV irradiation to remove gaseous contaminants.

Background

Conventional air purifiers that incorporate adsorbent beds to remove gaseous pollutants are typically short-lived and non-regenerable. This means that the adsorbent bed needs to be replaced periodically. Obee et al (US6,358,374) discloses an integrated air purification system comprising a catalyst bed, a UV source and a regenerable adsorbent bed to exert photocatalytic oxidation activity. It applies the Langmuir-Hinshelwood kinetic concept to such systems, so that the oxidation rate is improved, even for relatively low levels of gas contaminants. However, the' 374 system requires additional heat to release the captured contaminants from the regenerable adsorbent bed into the fixed volume chamber. Another disadvantage is that the oxidation rate of the titania-based catalyst in the present system is limited by the type of contaminant, the amount of each adsorbed contaminant, and the rate at which the adsorbed contaminant is released from the adsorbent bed. It does not provide a continuous air purification system even if the adsorbed contaminants reach a saturation level that triggers the regeneration cycle of the adsorbent bed.

Bohlen et al (US2011/0033346a1) also disclose air purifier channels in air purifiers having photocatalytic oxidation substrates activated by UV-a irradiation. The substrate includes three coatings of VOC decomposing catalyst, ozone decomposing catalyst and titanium oxide, respectively. Although the substrate has different coatings with different functions, the efficiency of photocatalytic oxidation and ozonolysis of gaseous pollutants is limited by the contact surface of each coating with the respective gaseous pollutant or ozone. The gas stream should pass through three coatings of the substrate to remove gaseous contaminants and excess ozone, and therefore, there is a need in the art for a single multifunctional coating having at least photocatalytic oxidation and ozonolysis activity, as well as a large contact surface area for an air purification system.

Disclosure of Invention

A first aspect of the present invention is directed to a system for removing gaseous contaminants comprising an enhanced multifunctional coating for oxidizing the gaseous contaminants. The coating comprises a single titanium dioxide (TiO) base for enhancing the photocatalytic oxidation of gaseous pollutants in the presence of a sufficient supply of ozone₂) The catalyst of (1). In exemplary embodiments, based on TiO₂The coating layer of (a) comprises a plurality of mesoporous structures having a pore size of 2-20nm so as to increase the total surface area (i.e. contact surface) of the catalyst. Ultraviolet radiation sources are also incorporated into the system to activate the TiO₂To perform efficient oxidation in the presence of a sufficient supply of ozone. Based on TiO₂The coating of (a) can be simultaneously activated under irradiation of UV light. Excess ozone is eliminated by the same multifunctional coating before the purified gas is exhausted from the system.

A second aspect of the invention relates to a method for removing gaseous contaminants from indoor ambient gas or gas from another source, such as an industrial exhaust source. The method includes passing the contaminated gas through a first filter containing a mass of randomly arranged glass fibers to remove particulates. The filtered gas is then mixed with ozone in a mixer chamber. The mixture of filtered gas and ozone is then oxidized by passing the mixed gas through a second filter comprising an enhanced multifunctional coating. Under UV irradiation, the photocatalytic properties of the titanium dioxide-based coating are then activated to enhance oxidation in the presence of a sufficient supply of ozone. At the same time, the excess ozone in the mixed gas is adsorbed on the multifunctional coating surface before the purified gas is discharged. The adsorbed ozone is then eliminated in situ to avoid any leakage into the environment after oxidation. The purified gas is then discharged, for example, into the space in which the purification system is located or into the atmosphere.

The system and method of the present invention operate and perform at ambient conditions, i.e., room temperature, atmospheric pressure, and relative humidity, respectively. The contaminant removal rate was from at least 82% to about 84% over a 5 minute run under continuous gas flow. Removable gas contaminants include, but are not limited to, NO_X、SO₂、H₂S, formaldehyde, NH₃. In addition to gaseous pollutants, Volatile Organic Compounds (VOCs) and organic odors can also be removed by the systems and methods of the present invention.

Drawings

FIG. 1 is a schematic diagram of a system for removing gaseous contaminants according to the present invention.

FIG. 2 is a graph of different conditions (i) UV only illumination; (ii) ozone only; (iii) nitric Oxide (NO) removal rate (2A) and nitrogen dioxide (NO) under UV irradiation in combination with ozone₂) A comparison of the rates (2B) is generated.

FIG. 3A is mesoporous TiO by BET surface analysis₂Pore size distribution of the film. FIG. 3B is a graph of mesoporous TiO on ceramic foam filter₂TEM images of the thin film.

Detailed Description

Fig. 1 illustrates an air purification system 10 of the present invention for the effective removal of gaseous contaminants from a source 15 through the use of an enhanced photocatalytic coating in conjunction with ozone pretreatment. In the exemplary embodiment, system 10 includes a first filter 20 for removing relatively large suspended particles, such as dust particles. The first filter 20 may be any known mechanical or electrostatic filter or combination thereof to remove one or more large suspended particles such as particulates.

In an exemplary embodiment, the system is also connected to an ozone generator 30 to provide sufficient ozone gas to the system. In one embodiment, the ozone generator may be an external unit connected to the system by a connecting tube. In another embodiment, the ozone generator may be integrated into the system. The ozone generator may be an ozone lamp, an ionizer, a plasma discharge device, or any device that can generate ozone. The mechanism for generating ozone gas typically involves passing atmospheric oxygen (O)₂) Ionization of molecules into ozone molecules (O)₃). Optionally, after the ozone gas produced by the ozone generator, the ozone gas is diluted using a zero order air generator in order to provide an optimal ozone concentration. Ozone is a powerful oxidant that can neutralize Volatile Organic Compounds (VOCs) and is also an antimicrobial agent that destroys or lyses microorganisms such as bacteria. Ozone can also remove gaseous odors.

In an exemplary embodiment, the system further includes a mixer chamber 35 for receiving the filtered gas from the first filter 20 and mixing the ozone gas from the ozone generator 30. The main purpose of mixing the filtered gas with ozone gas is to provide an adequate ozone source for the TiO-based gas in the present invention included therein₂Is oxidized in the multifunctional coated second filter 40. In a preferred embodiment, the concentration of ozone gas is about 5ppm and the holding time for mixing the ozone gas with the contaminated gas in the mixing chamber 35 is about 20 seconds. The mixing chamber 35 is preferably made of stainless steel to avoid any oxidation of the inner contact surface by ozone gas. The mixing chamber 35 also preferably incorporates a mixer chamber fan 37 that rotates at about 600rpm to facilitate mixing of the ozone gas with the contaminated gas within the mixing chamber 35. The flow rate of the mixed gas from the mixing chamber 35 to the second filter 40 is further monitored by a flow meter 32 connected at one end to the mixing chamber 35 and at the other end to the second filter 40. Ozone in the mixer chamber 35 may also be optimized prior to passing into the second filter 40A small degree of oxidation of the gaseous contaminants. The excess ozone will be eliminated in situ by the second filter 40 at a later stage by the photo-catalytic reaction of the surface of the same coating.

Depending on the overall configuration of the air purification system 10, multiple fans, such as mixer chamber fans 37, may be placed at locations throughout the system 10 in order to efficiently pass contaminated air through the system 10 in a suitable volume to facilitate contaminant removal. Similarly, more than one flow meter 32 may be placed at different locations throughout the system 10 to monitor the flow rates of different gases.

After the filtered gas is mixed with ozone gas in the mixer chamber 35, the mixed gas flows through the flow meter 32 into the mixer chamber with titanium dioxide (TiO) based integral₂) In the second filter 40 of a single photocatalytic coating. In exemplary embodiments, based on TiO₂The coating of (a) comprises titanium dioxide and optionally one or more metals selected from Ti, Zn, Cu, La, Mo, W, V, Se, Ba, Ce, Sn, Fe, Mg or Al and/or alloys and/or oxides thereof. Based on TiO₂The photocatalytic properties of the coating are derived from a coating having a thickness of 500. mu.W/cm²Irradiation of the UVA light pipe 45 at intensity activates. The UVA light source may be a bulb of UV light, a UV LED or any light source that can emit UV radiation at a wavelength from 320nm to 400nm, more preferably 365 nm. Based on TiO₂The coating of (a) activates a second oxidation of the gas contaminants in the presence of sufficient ozone supply and UV irradiation. Another function of the coating is to eliminate excess ozone, since such a coating also has an activity to decompose ozone. The in situ elimination of excess ozone can avoid leakage of these reactive molecules along with the purified gas. After passing through the second filter 40, the purified gas can be exhausted back through the exhaust 50 into the same indoor environment in which the contaminated gas was collected or into another environment such as another enclosed environment or the atmosphere.

The method for removing gaseous contaminants of the present invention follows a substantially similar workflow of the system as described in fig. 1. However, it will be appreciated that any modification in the system which results in the same technical effect, in accordance with the method of the invention, will fall within the scope of the invention.

In an exemplary embodiment, a method of purifying a contaminated gas comprises: (i) collecting contaminated gas from a source or indoor environment to a first filter; (ii) filtering the large suspended particles through a first filter; (iii) passing the filtered gas into a mixer chamber to mix the filtered gas with ozone gas generated from an ozone generator; (iv) passing the mixed gas from the mixer chamber to a second filter incorporating a single multifunctional coating; (v) irradiating the single multifunctional coating by a UV source to oxidize the gaseous contaminants while eliminating excess ozone from the mixed gas by the same single multifunctional coating to yield a purified gas; (vi) the purified gas is discharged from the second filter into the same indoor environment or into another enclosed area or into the atmosphere by circulation. In a preferred embodiment, the process is carried out under ambient conditions. The ambient conditions refer to the ambient temperature, atmospheric pressure and relative humidity, or atmosphere at the location where the method is carried out. In further embodiments, the method is suitable for use under different conditions such as elevated temperature, elevated atmospheric pressure and/or higher relative humidity as desired. In these cases, additional methods for removing moisture or excess heat from the input gas stream may be integrated into the overall process.

FIG. 2 is a graph showing a comparison of exemplary contaminant Nitric Oxide (NO) abatement (FIG. 2A) and nitrogen dioxide (NO) by using the system of the present invention under different conditions₂) A plot of the results of the experiment (fig. 2B) versus time was generated. These conditions are: (i) ozone only; (ii) UV only; and (iii) ozone in combination with UV. In this test, a gas sample having a predetermined concentration of a target contaminant is provided to the system of the present invention. Gas samples are continuously collected at the downstream part of the system over a period of time, e.g. 1 hour, to measure NO and NO at each time interval₂And (4) concentration. NO and NO₂The concentration reflects the oxidation efficiency of the system under different conditions.

In FIG. 2A, the NO concentration was reduced by about 16-18% under ozone only treatment and about 63-65% under UV only treatment during the first 15 minutes of the experiment. The NO concentration was reduced by about 82-84% in the first 5 minutes under the combined UV and ozone treatment compared to these single source treatments. The results show that systems incorporating the multifunctional coating of the present invention can significantly reduce the levels of contaminants such as NO under a combined UV and ozone treatment. This also demonstrates the synergistic effect of ozone and UV in the presence of the multifunctional coating.

In FIG. 2B, NO₂The concentration remained at a relatively low level until a later time point within 15 minutes prior to the experiment. From this point onwards, from NO to harmful NO₂Begins to rise as photocatalytic oxidation occurs on the multifunctional coating. In contrast, NO by UV-only treatment₂Production is highest due to lack of external ozone supply (only a limited number of O-radicals are produced by UV irradiation); NO by ozone treatment only₂The generation is the next highest among 3; NO produced by a combination of ozone and UV treatment₂And the lowest. In summary, NO is converted to harmful NO in the presence of both ozone and UV radiation₂The conversion of (b) is minimal, since most of the NO appears to be primarily based on TiO by the inventive multifunctional₂Is oxidized to nitrate, thus converting NO from NO₂The amount of (c) is low. In addition, NO₂Can be further oxidized by ozone to form nitrates. Thus, harmful NO and NO in the presence of both ozone and UV radiation₂The lowest total concentration.

FIG. 3A shows mesoporous TiO₂Pore size distribution of the film. TiO 2₂The pore size of the film was about 4 nm. FIG. 3B shows TiO composed of small particles with pore sizes of about 4-5nm₂An image of the film. Mesoporous TiO 2₂The coating not only has a large surface area and maintains a high photocatalytic activity, but also can provide more active sites for carrying out catalytic reactions in air purification.

If desired, the different functions discussed herein may be performed in a different order and/or concurrently with each other. Furthermore, if desired, one or more of the above-described functions may be optional or may be combined.

Although aspects of the invention are described in the independent claims, other aspects of the invention comprise other combinations of features from the described embodiments and/or the dependent claims with the features of the independent claims, and not solely the combinations explicitly described in the claims.

It is also noted herein that while the above describes example embodiments of the invention, these descriptions should not be viewed in a limiting sense. Rather, several variations and modifications are possible without departing from the scope of the invention as defined in the appended claims.

INDUSTRIAL APPLICABILITY

In contrast to conventional air purifiers, the present system, integrated with a multifunctional coating, combined with ozone and UV irradiation, provides the following features in one unit: (1) enhanced oxidation efficiency, (2) conversion of gaseous pollutants to gases that are harmless to both the human body and our environment, and (3) a single catalyst coating that is relatively durable, low cost, and compatible for multiple functions. It is suitable for mass production for different applications, such as air conditioning systems, humidifiers and dehumidifiers, industrial processes requiring air purification and controlling ozone emission.

Claims (16)

1. A system for removing particulate and gaseous contaminants from a gas stream, comprising:

a first filter for removing large suspended particulate matter from the gas stream to produce a first filtered gas;

a mixer chamber for mixing the first filtered gas with ozone gas to produce an ozone-enriched first filtered gas;

an ozone generator for providing the ozone gas to the mixer chamber;

TiO-based compositions incorporating a single multifunctional function₂Coating ofThe second filter of (1); and

for incorporating said TiO-based material₂A UV generator for generating UV in the presence of said second filter of the coating,

wherein the mixer chamber, the UV generator and the TiO-based₂Is configured to expose the ozone-enriched first filtered gas to the multifunctional TiO-based₂And UV light generated by the UV generator, and wherein the UV generator is selected from a UV lamp or UV LED emitting UV light with a wavelength of 320nm to 400nm, and wherein the ozone and UV light are at the second filter the multifunctional TiO based₂In the presence of a coating comprising a plurality of mesostructures in contact with the ozone-enriched first filtered gas to oxidize 82% to 84% of the gaseous pollutants to harmless gases within 5 minutes.

2. The system of claim 1, wherein the first filter comprises a mass of randomly arranged glass fibers.

3. The system of claim 1, wherein the mixer chamber is made of stainless steel.

4. The system of claim 1, wherein the ozone generator is either external to the mixer chamber or integrated into the mixer chamber, and the ozone generator is selected from an ionizer, a plasma discharge source, or a combination thereof.

5. The system of claim 1, wherein the mixer chamber comprises a ventilator that rotates at a speed of 600rpm for mixing filtered gas from the first filter with the ozone from the ozone generator for 20 seconds.

6. The system of claim 1, wherein the multifunctional TiO-based₂The coating of (a) is an oxidized photocatalyst and further comprises one or more of Ti, Zn, Cu, La, Mo, W, V, Se, Ba, Ce, Sn, Fe, Mg or Al, or an oxide thereof, or an alloy thereof.

7. The system of claim 1, wherein the multifunctional coating is an ozone decomposing element and further comprises one or more of Ti, Zn, Cu, La, Mo, W, V, Se, Ba, Ce, Sn, Fe, Mg, or Al, or oxides thereof, or alloys thereof.

8. The system of claim 1, wherein each of the plurality of mesoporous structures has a pore size of 2-20 nm.

9. The system of claim 1, wherein excess ozone in the ozone is decomposed by the multifunctional coating after oxidation.

10. The system of claim 1, wherein the gaseous contaminant comprises NO_x、SO₂、H₂S, formaldehyde, NH₃VOC and ozone.

11. The system of claim 1, wherein any portion of the system operates at ambient conditions.

12. A method for removing particulates and gaseous contaminants from a gas stream, comprising:

collecting the gas stream from an indoor environment or from an external source to produce a collected gas;

filtering the collected gas with a first filter to remove large suspended particles, producing a first filtered gas;

mixing the first filtered gas with ozone generated from an ozone generator to produce an ozone-enriched first filtered gas;

oxidizing the ozone-enriched first filtered gas with a second filter that incorporates a multifunctional TiO-based₂And a UV source having a wavelength of 320nm to 400 nm;

eliminating excess ozone after the second filter is subjected to the oxidizing to generate a purified gas; and

discharging the purified gas back into the indoor environment or to the source of the gas stream or to the atmosphere,

wherein the oxidation is of the ozone and UV light generated by the UV source at the multifunctional TiO-based₂To reduce the level of said gaseous pollutants by 82 to 84% in 5 minutes.

13. The method of claim 12, wherein said filtering of said collected gas is through said first filter comprising a mass of randomly arranged glass fibers to remove large suspended particles including said particulates to produce said first filtered gas.

14. The method of claim 12, wherein the mixing of the first filtered gas comprises providing ozone gas from an ozone generator to the mixer chamber at a speed of 600rpm for 20 seconds at ambient temperature, atmospheric pressure, and relative humidity.

15. The method of claim 12, wherein said elimination of said excess ozone is by said multifunctional TiO-based₂Is carried out in situ after said oxidation at ambient temperature, atmospheric pressure and relative humidity.

16. The method of claim 12, wherein the oxidizing is by increasing the multifunctional TiO-based₂Further enhanced by the total surface area of the coating comprising a plurality of mesostructures having a pore size of 2-20nm, such that 82% to 84% of the gaseous contaminants are removed within 5 minutes.